Transformers?

Question

A transformer is designed to step down the applied voltage of 120 V (rms) to 24 V (rms) at 60Hz. Calculate the maximum rms voltage that can be applied to the high-side of this transformer without exceeding the rated flux density in the core if this transformer is used in a power system with a frequency of 50Hz.

Answer 1

You cant calculate the maximum voltage from the information given, but you can estimate that if the ratio of voltage to frequency applied at 50 Hz is the same as the ratio of the rated voltage to frequency at 60 Hz the rated flux density will not be exceeded. That is 50Hz X 120V / 60Hz = 100V, so 100V would be acceptable.

Answer 2

I think there is some information missing from what you gave us, so you'll have to solve the numerical problem yourself. You need to use the formula for the magnetic flux density given the turns ratio, voltage, frequency and area of the core:

V=4.44 f N a B

See http://en.wikipedia.org/wiki/Transformer or core manufacturer websites for this formula. You will need to calculate the turns ratio, but that's pretty easy since you know it steps down 120V to 24V

Answer 3

Most transformer manufacturers make dual/rated (50/60 Hz) transformers. Calculation of saturation currents at each frequency requires a lot more data than you have provided. It is likely that increasing primary voltage would exceed current ratings before driving one of these transformers into saturation.